This invention relates to code identification apparatus of the type in which an instrument such as a key or card having a code recorded on it is submitted to a reader which reads the recorded code. Apparatus of this type may be used in locking systems and various accounting and credit control facilities. In the case of a locking system the reader will control the condition of a lock and the coded instrument would normally be in the form of a key which is inserted into the reader. In the case of credit control systems, the instrument would usually be in the form of a coded card.
The invention has particular, but not exclusive, application to apparatus in which the instrument is magnetically coded, for example by the inclusion of small magnets at selected locations within a non-magnetic body of the instrument. More specifically, it provides apparatus which is a logical development of the apparatus disclosed in U.S. Pat. No. 4,134,539.
U.S. Pat. No. 4,134,539 discloses an apparatus in which the code data on the instrument is read off row by row during key entry in synchronism with a strobe generated by the interception of light beams by the instrument which determines the position of the instrument. One problem encountered with this apparatus is that it is difficult to completely weatherproof since the light beams can be affected by dirt and dust and the focal length of the light devices can be changed by water introduced into the reader, for example by wet keys or cards. Moreover, due to the need for the light beams to be switched in sequence, a large number of wires are required between the reader and its control logic. The present invention provides an alternative kind of apparatus which avoids these problems.